1) Field of the Invention
The present invention relates to a vehicle passenger detecting apparatus which makes a decision on a state of a passenger (including a driver) sitting on a seat of a vehicle and transmits the state information to a vehicle passenger protecting apparatus.
2) Description of the Related Art
So far, there has been proposed a vehicle passenger detecting apparatus in which a load sensor is placed under a vehicle seat to detect a variation of pressure stemming from a passenger load for making a decision on a state of a passenger. In such a apparatus, a drift of the measurement reference (standard) for load sensor output can occur due to the mechanical accustomization of a load sensor and a seat component, applied mechanical repeated vibrations, applied mechanical impacts, environmental variations such as variations of temperature and humidity, and aging. In addition, when a drift of the measurement reference occurs, difficulty is experienced in making an accurate decision on the passenger state through the use of that load sensor. Therefore, for the accurate decision on the passenger state, there is a need to correct an unoccupied-seat reference serving as a measurement reference by precisely detecting an unoccupied seat and detecting a variation of an 0-kg load output.
So far, in consideration of such objects, there has been proposed a technique in which, in addition to a load sensor placed under a seat, a mat-type passenger presence/absence discrimination sensor is placed under a surface of a hip-supporting portion of a seat to make a decision/detection on an unoccupied state of the seat and, when a passenger is absent on the seat, a correction is made with respect to the measurement data from a load sensor (see Japanese Patent Laid-Open No. 2000-302003). This conventional technique can precisely detect the fact that a seat is in an unoccupied state, thereby correcting an unoccupied-seat reference.
There is a problem which arises with the conventional technique disclosed in Japanese Patent Laid-Open No. 2000-302003, however, in that the employment of the unoccupied-seat discrimination sensor and the load sensor increases the number of components of a vehicle seat, which leads to increasing the number of assembling steps and the cost of parts.